1. Field of the Invention
This invention relates to an ink jet recording apparatus and, more particularly, to an ink jet recording apparatus capable of reducing the possibility of an ink droplet ejection failure or malfunction and capable of performing recording with stability. The recording apparatus of the present invention can be applied to various office machines and communication apparatuses, such as electronic typewriters, word processors, copying machines, facsimile machines and computers.
2. Description of the Prior Art
Conventionally, recording apparatuses for recording on recording mediums, such as paper and overhead projector sheets (hereinafter referred to as recording sheets), have used recording heads that operate in accordance with various recording methods, such as wire dot methods, thermosensing methods, thermal transfer methods and ink jet methods. Ink jet methods, in which ink is directly jetted to a recording sheet, have attracted attention because they have a Low running cost and provide a low-noise recording operation.
In recent years, film-forming techniques and micromachining techniques for manufacturing semiconductor devices have been applied to the manufacture of ink jet recording apparatuses and, in particular, to ink jet recording heads, so that smaller and lower-priced recording heads are now being developed. Throw-away type recording heads integrally combined with ink tanks have also been provided. With such recording heads, smaller and simpler recording apparatuses are possible.
On the other hand, ink jet recording units having the above-described various advantages are being widely used as recording units of various kinds of apparatuses, such as electronic typewriters, word processors, facsimile machines and copying machines. Ink jet recording units for use in such apparatuses are designed to have constructions corresponding to the specific functions and modes of use of the respective apparatuses. Also, with respect to electronic typewriters, word processors and the like, there is a design trend to smaller, lighter and portable machines. In this respect as well, it is desirable to design smaller ink jet recording units with simpler constructions for use in these kinds of recording apparatuses.
Ordinarily, ink jet type recording apparatuses have a recording head with an array of fine ejection holes and are therefore designed to perform a process for removing the cause of an ejection failure (ejection recovery process), for example, in a case where air bubbles or dust particles enter the ejection holes or the state of the ink is changed by an increase in the viscosity caused by evaporation of the ink solvent so as to be unsuitable for recording. A means for performing such an ejection recovery process is known which includes a cap capable of covering the surface of the recording head in which the ejection holes are formed and serving as an ink receiver, and a pump communicating with this cap and capable of producing a suction force.
In an ink jet recording apparatus using such a means, ink is ejected by driving energy generation elements inside the ejection holes, while the cap is set so as to face the ejection hole formation surface, or ink is drawn from the ejection holes to remove the cause of an ejection failure by operating the pump to produce a suction force inside the cap while it is covering the ejection hole formation surface.
The operation of covering the ejection hole formation surface with the cap is typically performed by moving a carriage on which the recording head is mounted to a home position when recording is finished, and then bringing the cap, which is capable of advancing or retreating at this home position, into abutment against the recording head so as to cover the ejection hole surface.
A waste ink tank for storing waste ink produced by the ejection recovery process is provided at a suitable position in the apparatus. To force ink received in the ejection recovery system (the cap, the pump and a waste ink tube for communication between the cap and the pump) during the ejection recovery process into the waste ink tank, an operation called idle drawing is performed by operating the pump while the cap is open to the atmosphere to draw ink together with air into the ejection recovery system. If waste ink introduced into the ejection recovery system by an ejection recovery process is left therein, it may solidify or leak from the cap to the outside. The idle drawing operation is effective in preventing such a problem.
If the operator turns off the power source for the apparatus during recording or when the recording head is completely closed with the cap, and if the apparatus is left in this state for a long time, the ejection holes of the recording head can be clogged by an increase in the viscosity of ink in the ejection holes, which causes an ink droplet ejection failure or malfunction when the apparatus is used again, thus resulting in a deterioration in printing quality. To avoid this problem, an ejection recovery operation may be performed automatically by drawing ink through the ejection holes each time the power source is turned on. However, if that is done every time the power source is turned on, the ink consumption rate is considerably increased, resulting in an increase in running cost, particularly if the power source is turned on and off frequently.
Also, the recording apparatus may be arranged in such a manner that a "soft switch" is provided as a main switch of the apparatus. Then, if the main switch is turned off while the head is not capped, the apparatus performs a power-off sequence to cut the power supply only after the ejection holes have been completely closed with the cap. In this case, however, the control process is made complicated by the necessity of using a soft switch, so that manufacturing cost is increased. Moreover, even if such a soft switch is provided, it is still possible in some circumstances that the power-off sequence will not be started and the apparatus will be left for a long time without closing the ejection holes with the cap, for example, if the AC power supply to the apparatus is cut by disconnecting the plug from the wall outlet instead of turning off the main switch.